Design, fabrication, and characterization of low-dimensional quantum devices

Abstract

The realization of a two-dimensional electron gas in semiconductor heterostructures due to advanced epitaxial growth techniques has led to novel high-speed devices such as modulation-doped field effect transistors and quantum well lasers. High resolution lithography and pattern transfer techniques now make it possible to further restrict the electronic motion to lower dimensions. A variety of interesting quantum confinement phenomena have been observed in these mesoscopic systems. This thesis describes the design principle, fabrication technique, and transport characterization of various low-dimensional quantum devices.

Nanostructure fabrication techniques are presented in detail in the thesis, from high resolution electron beam lithography, pattern transfer techniques, to various one-dimensional (1D) and zero-dimensional (0D) structures with dimensions in the nanometer scale. The effective wire width as well as sidewall damage for both deep etched and shallow etched quantum wires are characterized by the electrical conductance measurement.

Artificial lateral surface superlattice (LSSL) structures of line and dot arrays are fabricated using multilayer resist techniques. A typical 1D quantized conductance of $\rm 2e\sp2/h$ is shown in an airbridge split gate device. Plateaulike transport characteristics are demonstrated in airbridge LSSL gate devices due to electrostatic confinement modulation. Laterally tunable single-gate quantum dot and double-bend quantum dot devices are fabricated and investigated. Negative differential conductance is observed at various drain bias conditions in both of these quantum dot devices. Conductance oscillations observed at a temperature as high as 10 K are, to our understanding, the highest temperature reported in similar laterally confined quantum dot devices.